The present inventor has spearheaded the adoption of electrical transient surge protectors in plug-in adapters inserted between the usual watt-hour meter and its socket, as disclosed in his issued patents and other copending patent applications identified above.
Similar protection against transient electrical surges may be installed instead (or in addition) at nearby upstream locations, such as a weatherhead, or downstream locations, such as a utility power panel, and may either be built-in or be added thereto in prepackaged form. Applicant's surge-protective apparatus utilizes varistors or equivalent non-linear resistance means as components in their usual disklike form, whether partially prepackaged or not.
A known type of downstream surge-protective device is often packaged in so-called "grenade" form. An example of such device is disclosed by Reitz as a "Secondary Arrester" in U.S. Pat. No. 4,439,807.
A common feature of packaged forms of surge protectors is lack of capacity to carry extreme current densities, such as often result on power lines, as from lightning. A metal oxide varistor can shunt considerable surge current to ground and thereby protect downstream equipment, but repeated surge conduction increases the likelihood of failure in associated equipment or in surge-protection apparatus itself, if cooling time and paths are inadequate. Varistors may get so hot therefrom as to reach a characteristic failure temperature, resulting in loss of physical integrity--perhaps explosively.
Rather than to rely upon the installers of prepackaged surge-protective equipment to provide adequate local fusing to protect it from possible overloading and failure, it is preferable to include in the package means to increase its current-carrying capacity, to inhibit its temperature rise, and lastly to disconnect it entirely.
The present inventor has pioneered increases in surge capacity and safety of such surge-protective apparatus by heat-sinking component varistors (as in the earliest filed of his above mentioned patent applications, to issue as U.S. Pat. No. 4,931,895); by inserting temperature-responsive or "thermal" fuses or similar cutoff devices to sense the temperature of the varistors and to disconnect them from the power lines in the rare but possible event of excessive temperature rise (as in his U.S. Pat. No. 4,866,560); by stacking varistor disks in parallel circuit therein (as in his U.S. Pat. No. 4,901,187); and by including distributed-resistance fuse links--with and without thermal cutoff means and/or varistor stacking--between power line leads and such varistors (as in his U.S. Pat. No. 4,907,119).
The present invention relates to extension of such improvements exemplified in a prepackaged (such as a "grenade" ) type of surge-protective apparatus but also suitable for use in a surge-protection device in a weatherhead, meter adapter, utility panel, or elsewhere.